I really liked the previous 2 themes by GTGraphics ( Space theme and GTGraphics 2) and their latest theme is a good one as well

GTGraphics 3 theme

GTGraphics introduces a fantastical element in their third free Windows theme, combining medieval cityscapes and gleaming white castles with their trademark illustrations of futuristic spacescapes and alien worlds”

GTGraphics 3 theme

Download GTGraphics theme for Windows


PS don’t forget all themes work in Windows 7, Windows 8, Windows RT and Windows 8.1